Apoptosis is a highly regulated form of cell death characterized by specific morphological, biochemical, and molecular events. However, its role during aging, particularly in post mitotic tissues such as the brain, heart and skeletal muscle has not been studied in depth. Apoptosis appear to increase in post-mitotic tissues with age and it may be a major contributing factor to the observed loss in tissue function with age. The mechanisms by which apoptosis are induced with advancing age and adaptations that may protect against apoptosis remain to be identified. Oxidants and calcium initiate a sequence of events that play a key role in the activation of the mitochondrial - and the endoplasmic reticulum-mediated pathways of cell death. We will endogenously increase levels of mitochondrial superoxide radical and also exogenously add hydrogen peroxide, peroxynitrite and/or calcium to isolated mitochondria in young (6-month) and old (24-month) rats. The activation and adaptive potential of the mitochondrial-mediated pathway and endoplasmic reticulum -mediated pathway will be investigated in vivo, in young and old rats, through the administration of both doxorubicin (increases mitochondrial superoxide) and thapsigargin (stimulates calcium release from the endoplasmic reticulum), causing an increase in apoptosis. Moreover, we will determine apoptosis and alterations in the activation of the apoptotic signal transduction pathways during normal aging, in 6-, 12-, 18-, 24- and 26-month old Fischer 344 rats, by studying regulatory proteins acutely activated to regulate apoptosis. We will use caloric restriction - an intervention that reduces oxidant production, improves calcium handling, reduces cell loss and extends maximum life span - to further study the anti-apoptotic adaptations. In addition, we will investigate skeletal and heart muscle function with age and relate this to apoptosis and the attenuation of apoptosis by caloric restriction. This approach will enable a greater understanding of the mechanisms of apoptosis in vivo during acute stress in young and old animals, normal aging, and caloric restriction.